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2 What makes a good detector? High bandwidth High efficiency Low voltage operation Low dark current CMOS compatibility Si Ge Silicon is not adapted for detection at 850nm, 1300nm, 1550nm. The growth of Germanium on silicon is still a challenge in terms of cost and complexity

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3 Proposed Device We carryed out the calculation of: QuantumEfficiency Bandwidth Dark current The bottom mirror could be a DBR fabricated using repeatedly a silicon-on-insulator process (SOI). On top of the DBR could be grown a n-Si layer and then deposited Schottky metal (Au in our simulations) which would be both the absorbing layer and top mirror of microcavity.

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4 Internal photoemission Advantages: - The design of device is completely compatible with ULSI silicon technology. - Fast devices Disadvantages: - The Internal Photoemission effect is very weak! Internal photoemission is the optical excitation of electrons in the Schottky metal to an energy above the Schottky barrier and transport of these electrons to the conduction band of the semiconductor (n-type in figure). The Internal photoemissio theory has been developed by Fowler R. H. Fowler, Physical Review, 1931, vol. 38, pp.45-56. V. E. Vickers, Applied Optics, vol. 10, No. 9, 1971, 2190-2192

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7 Intrinsic device bandwidth The intrinsic limit of the device is: where: - v t is the silicon drift velocity - L is the λ/2-cavity thickness The device is very fast, being the metal the absorbing layer, the semiconductor can be made very thin. By improving the inverse voltage a 0.1 GHz bandwidth-efficiency product was obtained. Inverse voltage applied [V] Bandwidth-Efficiency product [GHz]

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8 Device dark current Dark current density [A/cm 2 ] Inverse voltage applied [V] Dark current is due to the thermal process and tunnelling process. For slightly doped silicon (<10 17 cm -3 ) and T300K the tunnelling current density, for a Au-Si barrier, can be neglected. - A * is the Richardson constant. - η c is the barrier escape probability. - ΔФ B is the potential barrier lowering. Device current density is given by: S. M. Sze, Physics of Semiconductor Devices, John Wiley & Sons, New York, 2nd ed., 1981 The high potential barrier allows to work at room temperature obtaining a dark current density of 5.5μA/cm 2.

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9 Conclusions In this communication, the design of a Si resonant cavity enhanced Schottky photodetector, based on the internal photoemission effect, operating at room temperature and working at 1.55 micron, is reported. Using Au-Si as Shottky barrier all the device performance were calculated in term of efficiency, dark current density and bandwidth. The device is intrinsically very fast and its efficiency can be enhanced by improving the inverse applied voltage untill to obtain an efficiency-bandwidth product of 0.1GHz. We are confident that it is possible to improve the performances of device considering high Q-value optical microcavities (disk resonators) in silicon waveguide.